1. Field of the Invention
The present invention relates to a sealing device and, more particularly, a sealing device including a seal ring and a backup ring in a mounting groove to gasoline fuel, oil, water or the like of high-pressure fluid.
2. Description of the Conventional Art
A conventional sealing device includes a seal ring such as an O-ring made of a rubber-like elastic body and a back up ring made of a resin or the like and positioned at a low pressure side of the seal ring in a mounting groove having a tapered groove bottom inclined in such the direction that a distance between the tapered groove bottom and a housing expands from a side end surface at a low pressure side provided on the shaft toward a high pressure side, to seal a part between a shaft hole formed at the housing and a shaft. In the conventional sealing device, when pressure of fluid is applied from the high-pressure side, the backup ring is pressed toward the low pressure side from the high pressure side through the seal ring. The backup ring has an inner peripheral surface formed with a tapered part, which corresponds to the tapered groove bottom of the mounting groove and is inclined in the same direction as that of the groove bottom. Further, the back up ring has an outer peripheral surface formed with a parallel surface which is parallel to an inner peripheral surface of the housing. When the inner peripheral surface of the backup ring contacts the tapered groove bottom of the mounting groove by pressure from the high pressure side, the outer peripheral surface of the backup ring tightly contacts to the inner peripheral surface of the housing by radial directional component force. Accordingly, a gap between the backup ring and the inner peripheral surface of the housing is closed so as to prevent protruding of the seal ring toward the low pressure side.
According to such the constitution, there is no problem when the sealing device is subjected to a general fluid pressure or an eccentricity of the shaft is small. However, when the device is subjected to high-pressure fluid or has an eccentricity of the shaft is large, a gap may be generated between an outer peripheral surface of a backup ring and an inner peripheral surface of a housing so as to protrude a seal ring toward a low pressure side. Therefore, Japanese Patent Application Laid Open No. 11-315925 proposes a device in which a gap g is provided between a side end surface 101a at a low pressure side L of a backup ring 101 and a side wall surface 102a at a low pressure side L of a mounting groove 102, as illustrated in FIG. 12.
Accordingly, when the device is subjected to high-pressure fluid, the backup ring 101 moves to the low pressure side L so as to generate radial directional component force. The radial directional component force reduces a gap between a tapered part of the backup ring 101 and the mounting groove 102 and a gap between an outer peripheral surface of the backup ring 101 and a housing 104. Further, in order to obtain an effect to reduce a gap, a technique that an outer diameter of a backup ring 101 is set to be equal to or larger than an inner diameter of a housing 104 so as to fit those has been considered.
However, as illustrated in FIG. 13, when an outer diameter of a backup ring 101 is set to be equal to or larger than an inner diameter of a housing 104, a side end surface 101b at a high pressure side H of the backup ring 101 contacts to a top end part 104A of a housing 104 at the time of inserting a shaft into the housing 104, so that a shaft insertion load increases. Further, since the shaft is inserted while the top end part 104A is contacted with the side end surface 101b, the backup ring 101 may be inclined and mounted in the state that inner and outer peripheral surfaces are not correctly in tight contact with opposite members. When being mounted in the above-described state, the backup ring 101 cannot realize the function of preventing protrusion of a seal ring 105, and the seal ring 105 is protruded toward a low pressure side when being subjected to high-pressure fluid, so that a device may be damaged. Therefore, when the shaft is inserted while the top end part 104A is contacted with the side end surface 101b, a device cannot realize a seal function.